1. Field of the Invention
The present invention relates generally to methods of manufacturing medical tubing. In particular, the present invention relates to methods of making catheters having a porous structure in which additives, such as therapeutic or diagnostic agents, can be carried.
2. Description of the Related Art
Medical tubing and catheters are widely employed for a variety of treatment and diagnostic procedures involving, for example, the administration of fluid medications and devices into a patient and the removal of fluids from the patient. In this application, the terms “catheter” and “medical tubing” will be used interchangeably to refer to the same structure.
The ultimate use for which medical tubing is designed requires that the tubing have certain physical characteristics. For example, a catheter must be sufficiently stiff or rigid to enable its insertion and movement through narrow body orifices and channels and, in some applications, must also be able to withstand a high bursting pressure. On the other hand, a catheter must be sufficiently soft and flexible so that it may readily conform to body shapes so as not to cause injury to the interior wall of a patient's vessel as it is advanced. In addition, a catheter must be of sufficient mechanical strength to resist tearing during normal use, such as when the catheter is removed against tissue resistance.
In many medical devices, the polymer used to construct these devices is first compounded with additional agents, such as coloring agents, plastisizers, and opacifiers to obtain optimum properties of the medical device for which the polymer is used. Such compounding generally involves adding the desired additive to pellets of the polymer and running the mix through a compounder (e.g., an extruder) where the polymer is sheared apart and inherently blends with the polymer. After manufacturing, the devices are often coated with things to reduce friction, improve blood compatibility, or provide therapeutic benefits. Such surface coatings are difficult to accomplish because the surface must be prepared correctly and the coatings are often rubbed or worn off.
The Applicant previously developed a method for nonextrusion manufacturing of catheters, which is described in U.S. Pat. No. 6,030,371. In this existing method, a catheter is formed by spraying a fine polymer particulate, or solvenated polymer particulate, over a core to form a polymer shell of the catheter. The polymer material can be varied over the length of the catheter by using different hardness polymers to gradually vary the hardness of the catheter. The '371 patent teaches that the different hardness polymers can be colored to provide visual confirmation of the transition of hardness. The '371 patent also teaches the application of an opacifier material with the polymer material, or between layers of the polymer material. The polymer and opacifier materials are consolidated, for example, by heating in an oven.
Existing catheter manufacturing methods have not recognized the significant advantages that can be obtained by developing a catheter having a porous structure that can be used to carry therapeutic agents, diagnostic agents, and/or other desired agents into a patient's body.